1. Field of the Invention
The present invention relates to an image processing device, an imaging apparatus, a parameter generating method, an image processing method, and a non-transitory computer readable recording medium storing a program for performing restoration processing and sharpening processing, and in particular, relates to a method of adjusting the restoration strength and the sharpening strength.
2. Description of the Related Art
In a subject image captured through an optical system, a point spread phenomenon may be observed in which a point subject has a very small spread due to the influence of diffraction, aberration, or the like caused by the optical system. A function showing a response to a point light source of the optical system is called a point spread function (PSF), and is known as a parameter affecting the resolution degradation (blur) of a captured image.
In a captured image having an image quality that has been degraded due to the point spread phenomenon, it is possible to recover the image quality by performing point image restoration processing based on the PSF. Point image restoration processing is a process of calculating the degradation characteristics (point image characteristics) due to the aberration of a lens that forms the optical system in advance and canceling out the point spread of a captured image by image processing using a restoration filter (recovery filter) corresponding to the point image characteristics.
If the imaging conditions or a lens is changed, the PSF is changed. Therefore, it is preferable to change a restoration filter used in the point image restoration processing whenever the imaging conditions are changed or a lens is replaced and to perform the point image restoration processing using the restoration filter corresponding to the new imaging conditions or the newly attached lens.
As a representative example of the restoration filter that can be used in the point image restoration processing, a Wiener filter is known. The point image restoration processing using the Wiener filter is a process that is determined mathematically uniquely if the optical transfer function (OTF) of the lens and the imaging system signal-noise ratio (SN ratio) that depends on a frequency are determined.
In addition to the point image restoration processing, image processing for improving the image quality may be performed. For example, it is possible to improve the sharpness of an image by sharpening processing (outline enhancement processing, edge enhancement processing, sharpness enhancement processing, and the like).
As a specific processing method regarding the point image restoration processing and the sharpening processing described above, for example, JP2011-123589A discloses image processing using an image recovery filter to reduce phase degradation components and an edge enhancement filter to reduce amplitude degradation components. JP2006-333061A discloses performing “image stabilization for performing edge enhancement processing after performing image restoration processing using an image restoration filter” and “image stabilization for simply performing edge enhancement processing”. JP2009-27750A discloses determining the degree of enhancement of outline components of a video signal according to conditions, such as a diaphragm at the time of imaging. JP2006-129236A discloses changing the strength of a restoration filter itself according to the edge strength by selecting filters having different restoration strengths according to the edge strength.